Thoughts on my wiring schematic?

[cloudy]

After a lot of reading of EV related forums, I'm putting together a schematic for my lightweight EV. Have settled on a small Tesla front drive with Damien control board and SimpBMS with tesla modules. Thinking of using LG Chem cells, as I only need ~15kwh but do need high voltage. Charger & DC-DC still undecided, perhaps these will simplify some of this wiring...

Posting up my diagram so far for discussion, or to perhaps help others. It's still work in progress and missing some things (such as charger contactors)

Some outstanding decisions:

- What part of the system is best to control the contactors - there is precharge and positive outputs on the drive unit, but no neg output (which I think some just drive off the ignition key) Not sure if low side switching outputs will work with economiser contactors either...

- In this setup with everything going through a HV junction box - during charge the drive unit would be powered with HV (the main contactors would need to be closed) bad idea?

- Should the BMS be always powered, or only during charge/discharge?

- Should the charger "AC detected" output power up the whole car? I guess drive enable should be interlocked during charge so it's not a security risk.

- How much cooling is the Tesla drive unit likely to need? Small car radiator enough, fan needed?

[johu]

- What part of the system is best to control the contactors - there is precharge and positive outputs on the drive unit, but no neg output (which I think some just drive off the ignition key) Not sure if low side switching outputs will work with economiser contactors either...

Didn't understand the entire question but low side outputs work with economizers, tested.

- Should the BMS be always powered, or only during charge/discharge?

The BMS might do balancing when idle, Tom might give you more input on that.

[cloudy]

Interesting on the economiser, thanks. The question was really just confusion over multiple places to drive them from...

BMS - It does appear to balance in "Ready" mode, as long as the cells are over the minimum balance voltage. Balancing is relatively slow, so maybe need to continue it even after a drive or charge...

[Kevin Sharpe]

Thinking of using LG Chem cells, as I only need ~15kwh but do need high voltage.

What voltage are you planning? If you go below ~200V you'll have issues with DC rapid chargers and Tesla chargers.

How much cooling is the Tesla drive unit likely to need? Small car radiator enough, fan needed?

I don't think we have any real data on this. On my bus we made provision for a large rad and fan with the idea that it's easy to turn off the fan

[tom91]

The SimpBMS can be powered all the time, working on having it work more reliably when switched (SOC currently lags a bit when switched on and off).

You mention SimpBMS with tesla modules and then LG chem 16s packs? can you explain what you are on about.

The TesLiner from Zero EV (large drive unit pushing well above its name plate rating) is cooled using an aluminium civic radiator like used in a lot of kit cars, fan is only needed due to its wierd location in the boot.

The most critical would be to have the forward and reverse signal intercepted (you could also just cut the power to the switches if you are using those) , by the BMS when a critical fault occurs. This could just easily be a relay powered from the BMS positive contactor output. This way you do not drop a contractor at speed, this would result in blowing up your inverter due to back emf not being limited down.

[cloudy]

Thinking 6x 2.6kWh chem cells in series - should give a nominal pack voltage of 365V

Tom, I'm planning on using the tesla modules rewired into the cell taps on the chem batteries - 2 fully populated boards and one with 4 cells - per pack to talk to all 16 cells. I've got this setup working on the bench with some 18650 cells to test.

Was planning on a polo sized aluminium rad, in direct airflow. I guess it's not generating any heat at rest, so as long as the cooling keeps up under movement, there shouldn't be a whole bunch of latent heat to dump whilst stationary...

[Kevin Sharpe]

Was planning on a polo sized aluminium rad, in direct airflow. I guess it's not generating any heat at rest, so as long as the cooling keeps up under movement, there shouldn't be a whole bunch of latent heat to dump whilst stationary...

What happens when you've been driving hard and come to a stop? That heat has got to go somewhere

[johnspark]

Would it be better to have the fuse in the middle of the pack, that way if there is a short circuit, your battery is immediately split into +365/2 and -365/2.

[cloudy]

Very good idea - I think toyota do something along these lines going by this, I guess this is still not rendered a safe voltage, but helps

[johnspark]

Cloudy that is exactly what they do. Battery pack voltage split in two, visible air gap for people working on the HV wires.

I have also bought a plug and socket with 50mm2 screened orange sheathed cable for connection from battery pack to inverter.

[joromy]

Hi Cloudy, have a working setup for the simp BMS, tesla charger and openinverter.
Maybe it can be useful for you?

https://www.openinverter.org/forum/view ... f=16&t=187

https://www.openinverter.org/forum/down ... php?id=701

[johnspark]

can't remember if i posted this before, but here is a recommended cable size for wires in cars.